CYP19A1 is an enzyme that catalyzes the formation of aromatic C18 estrogens from C19 androgen. In humans, a number of tissues have the capacity to express aromatase, including the ovaries and testes, the placenta and fetal liver, adipose tissue, chondrocytes and osteoblasts of bone, the vasculature smooth muscle, and numerous sites in the brain, including several areas of the hypothalamus, limbic system, and cerebral cortex.